Selective oxidation of sulfides to sulfoxides or sulfones using Keggin heteropolyacid as catalyst

P. TUNDO, G. ROMANELLI, P. DIMITROFF, P. VÁZQUEZ

Dresden, Alemania

Conferencia; 1st International IUPAC Conference on Green Chemistry; 2006

IUPAC

Currently there is considerable interest in exploiting both the structure of catalyst precursors and the multicenter active sites to facilitate catalysis by polyoxometalates. Thus, it is very important to use fully characterized and more reliable catalyst precursors for catalytic reactions. The Keggin family has attracted much attention particularly because they provide a good basis for the molecular design of mixed oxide catalysts and high capabilities in practical uses. On the other hand, H2O2 is one of the oxidants frequently used in fine chemicals synthesis since its use leads to a cleaner technology because, principally, its reaction produces only H2O as by-product. In relation to selective oxidation, the reaction of sulfides to sulfoxides has been a challenge for many years, owing to the importance of sulfoxides as intermediates in organic synthesis. Sulfones are also important compounds employed in the preparation and functionalization of a wide variety of products by stabilizing a-radicals, a anions and acting as cationic synthons.  The objective of this work was studied the influence of H5PMo11Al0.5V0.5O40 (HPA), with Keggin structure, as catalyst in selective oxidation of sulfides to sulfoxides or sulfones, with H2O2. High conversion and excellent selectivity was obtained to sulfoxides or sulfones, using the reaction conditions showed in Scheme 1, the amount of catalyst used was 1 % (mmol) in relation to initial reactive. The better reaction conditions for selective oxidation of methyl phenyl sulfide to sulfoxides 2, with H2O2 were: room temperature, ratio of 1:28 of molar sustrate to H2O2, acetonitrile as solvent and 1 % HPA (in mmol) as catalyst. 100 % of conversion by reactive, for 1 h of reaction time, with 99 % of selectivity to sulfoxides 2 were obtained for previously described reaction conditions. In addition, the better reaction conditions for selective oxidation of methyl phenyl sulfide to sulfone 3 (100 % selectivity and conversion, respectively) was obtained for 2 h of reaction time. The V presence on Keggin structure is very important to obtain both products. In order to establish general applicability of experimental conditions various functionalized sulfides were subjected to the oxidation protocol.